The present invention is related to capturing messages in a signaling network, and more particularly, to capturing and correlating messages from an A interface in a GSM network.
The Global System for Mobile Communications (GSM) is the standard for a second generation cellular system. Although it was initially developed as a common mobile communications system in Europe, GSM systems are now deployed world-wide. The GSM standards, which specify network level architectures and services, are set by the European Technical Standards Institute (ETSI). In a GSM system, Mobile Stations (MS) communicate with a Base Station Subsystem (BSS) via a radio interface or air interface xe2x80x9cUmxe2x80x9d. BSSs are connected to Mobile Switching Centers (MSC) through an xe2x80x9cAxe2x80x9d interface, which may be embodied as dedicated or leased wirelines or a microwave link.
The GSM BSSs are comprised of a number of Base Transceiver Stations (BTS) each coupled to a single Base Station Controller (BSC). The Um air interface exists between the BTSs and the individual MSs. The interface between a BTS and the BSC is designated the Abis interface. The BSS is responsible for channel allocation, power control, signaling, handover initiation and other functions. The MSC functions include handover control, MS location updating and paging. MSCs also provide a gateway to other networks, such as the Public Switched Telephone Network (PSTN), Integrated Services Digital Network (ISDN) and packet data networks.
The A interface has a well defined protocol in the GSM system so that service providers and network operators can connect BSSs and MSCs from different manufacturers for use in the same system. The A interface uses the Signaling System No. 7 (SS7) Signaling Correction Control Part (SCCP) protocol to support communication between the MSC and the BSs and between the MSC and the MSs. The signaling protocol on the A interface consists of three layers. The first layer, or the Physical Layer, is a digital trunk. The digital trunk is coupled to a traffic channel on the Um air interface to convey speech and data between the MSC and MS. The Data Link Layer (Layer 2) consists of the Message Transfer Part Level 2 (MTP2) of SS7. MTP2 provides reliable transfer of signaling messages between the MSC and BS. The Message Layer (Layer 3) consists of the Base Station Subsystem Application Part (BSSAP).
BSSAP uses the SCCP protocol and consists of two parts: the Direct Transfer Application Part (DTAP) and the BSS Management Application Process (BSSMAP). At a BSS, DTAP transparently transfers Mobility Management (MM) messages and Connection Management (CM) messages between the MSC and MSs. The DTAP messages are not processed by the BSS. MM messages support MS location updating and authentication. CM messages support Call Control, Supplementary Services and Short Message Service (SMS). The Call Control sublayer contains messages for the set-up and release of connections to the MS. SMS allows users to send short text messages to the MS for display to the subscriber. BSSMAP messages relate to communications between the MSC and the BSC, such as Radio Resource management (RR) messages. The BSSMAP messages support all of the procedures between the MSC and the BSS, such as resource allocation, paging, handover, and release.
The GSM mobiles, or Mobile Stations (MSs), consist of two parts: the Mobile Equipment (ME) and the Subscriber Identify Module (SIM). The ME comprises the transmitter, receiver, keypad, microphone, speaker, etc. The SIM is a smart card that stores information about the ME user. The SIM can be used with any ME and the ME is operable only when the SIM is inserted. An MS is uniquely identified by its International Mobile Station Identity (IMSI). The IMSI identifies both a Public Land Mobile Network (PLMN) selected by the user for mobile service and a specific MS within the PLMN. The IMSI is assigned by the PLMN service provider and is stored in permanent memory on the SIM. MSs are also identified by a Temporary Mobile Station Identity (TMSI). A TMSI uniquely identifies the MS within a location area of a PLMN using a 32-bit binary number. Location areas consist of a number of adjacent cells in a PLMN. The TMSI is stored in temporary memory on the SIM. TMSIs provide protection against fraudulent use of MS identities because an intercepted TMSI does not identify the MS after it has left a location area. Most messages identify the MS by a TSMI and a Location Area Identity (LAI).
Related, co-pending application Ser. No. 09/092,771, filed Jun. 5, 1998, which issued as U.S. Pat. No. 6,411,604 on Jun. 25, 2002, entitled SYSTEM AND METHOD FOR CORRELATING TRANSACTION MESSAGES IN A COMMUNICATIONS NETWORK, discloses a monitoring system for capturing and correlating all of the messages for a single transaction in a communication or signaling network, such as an SS7 network. Other applications, including application Ser. No. 09/057,940, entitled SYSTEM AND METHOD FOR MONITORING PERFORMANCE STATISTICS IN A COMMUNICATION NETWORK, filed Apr. 9, 1998, which was issued as U.S. Pat. No. 6,028,914 on Feb. 22, 2000; application Ser. No. 09/092,699 entitled SYSTEM AND METHOD FOR SIGNAL UNIT DATA STORAGE AND POST CAPTURE CALL TRACE IN A COMMUNICATIONS NETWORK, filed Jun. 5, 1998; application Ser. No. 09/093,824 entitled TRANSACTION CONTROL APPLICATION PART (TCAP) CALL DETAIL RECORD GENERATION IN A COMMUNICATION NETWORK, filed Jun. 8, 1998, which issued as U.S. Pat. No. 6,249,572 on Jun. 19, 2001; and application Ser. No. 09/093,955 entitled SYSTEM AND METHOD FOR MONITORING SERVICE QUALITY IN A COMMUNICATION NETWORK, filed Jun. 8, 1998, which issued as U.S. Pat. No. 6,381,306 on Apr. 30, 2002, also disclose systems and methods for capturing and correlating call and transaction messages in a communication network. These applications are commonly assigned and hereby incorporated by reference herein.
It is known in the prior art for monitoring systems to be coupled to the communication links in a wireline network. The monitoring systems disclosed in the prior art capture the Signaling Units (SU) and messages that pass across the communication link. The systems then correlate the call and transaction messages captured from various links into call and transaction records. System operators can access these records to monitor calls or transactions for particular subscribers or to troubleshoot network problems. The call and transaction records can also be used to generate network and performance statistics. However, the prior art does not teach a system or method for capturing and correlating messages from the links between components in a wireless network. In the case of a wireless network, such as a GSM network, the prior art methods of correlating call or transaction messages will not work because a MS may change BTSs, BSCs, and even MSCs during the course of a single call as the MS moves from one cell to another. Accordingly, there is a need in the art for a system and method in which all of the messages that are related to a single GSM call can be captured and correlated into a single record.
It is an object of the present invention to capture all of the signaling units from the A interfaces for an MSC and to correlate messages that belong to a single mobile call into a call record.
It is a further object of the present invention to correlate messages for a single call as the call is handed over among two or more BSCs served by the MSC.
It is another object of the present invention to correlate mobile call messages captured from A interface links with related call and transaction messages that are captured on other communication links.
It is another object of the present invention to correlate messages based on SCCP connections.
These and other objects, features and technical advantages are achieved by a system and method which correlates signaling units captured from A interface links in a GSM network so that all messages for a particular call, including messages on different A interface links due to handover, are combined into a single call record.
Monitoring units capture messages from all of the communications links of an MSC, including the A interface links between the MSC and various BSCs. The captured messages are routed by link processors to call, transaction and A interface processors based upon the message type. A interface processors create an Anchor Transit Record and a Call Record upon detecting the initial message for a new call connection. Any messages having the same Originating Point Code (OPC) and Source Connection Reference number as the initial call connection message are added the Call Record by the Anchor Transit Record. A Secondary Transit Record is created using the response to the initial call connection message. The Secondary Transit Record routes all messages for the call to the Anchor Transit Record, which adds the messages to the Call Record.
When a call is handed over to a new BSC, a Handover Pending Transit Record is created. The Handover Pending Transit Record is promoted to either a Handover Router or an Anchor Transit Record depending upon whether or not the handover connection can be coordinated with another A interface connection having an existing Anchor Transit Record. Handover Connection Records are created when an existing A interface call is handed over or when a new A interface call connection is initiated for a hand over call. If the Handover Connection Records are correlated by a rendezvous processor, then the Handover Pending Transit Record is promoted to a Handover Router and it routes all related messages to the original Anchor Transit Record for the handover-from connection. The original Anchor Transit Record is promoted to a Handover Anchor Transit Record and it adds all messages from both the handover-from and handover-to sides of the connection. Eventually the connection on the handover-from side is torn down and the Secondary Transit Record is destroyed because it is no longer needed.
On the other hand, if the connection on the handover-from side was associated with a different MSC, then the Handover Connection Record will not be correlated by the rendezvous processor and the Handover Pending Connection Record will be promoted to a new Anchor Transit Record. A new Call Record will also be created to collect the messages for the handover-to connection.
Additional Handover Pending and Handover Router Transit Records will be created as the call is handed over to other A interfaces. The Handover Anchor Record continues to route messages to the Call Record as long as the connection is maintained by the MSC. When the call is terminated or when the call connection moves to another MSC, the Handover Anchor Record is terminated and the Call Record is passed to a central server, or other device, for additional processing in real-time while the call continues on the second MSC.
The central server may correlate the completed A interface Call Record to A interface Call Records for the same or other MSCs. Additionally, the completed A interface call record may be correlated to other call and transaction records from other networks to create a global call record which includes all of the call and transaction messages for a particular call.
It is a feature of the present invention to capture all of the messages from the A interfaces of an MSC in a GSM network. A single monitoring unit is coupled to each A interface link so that messages belonging to a particular call may be captured from each A interface.
It is another feature of the present invention to maintain an anchor record for routing messages to a call record using the primary OPC and source connection reference for messages.
It is a further feature of the present invention to maintain a secondary record for routing certain messages to the anchor record using the alternate point code and source connection reference for messages.
It is another feature of the present invention to create a handover pending record when a new handover connection is detected on an A interface link. If the new handover connection is correlated to an existing anchor record, then messages for the handover connection are routed to the anchor record by converting the handover pending record to a handover routing record. If the handover connection is not correlated to an existing anchor record, then the handover pending record is converted to a new anchor record.
It is a feature of the present invention to correlate all messages related to a specific call into a single call record without regard to which A interface the message is detected on by using the cell identifier and handover reference number carried in certain messages.
It is an additional feature of the present invention to correlate a connection on a first A interface with a connection on a second A interface by using handover connection reference records comprising information that identifies a specific handover event.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying put the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.